Sepsis is a very serious response to an infection. Infection causes an inflammatory response. If a patient develops a widespread inflammatory response, it is called Systemic Inflammatory Response Syndrome or SIRS. If the patient has SIRS that is caused by an infection, the patient has "Sepsis".

Systemic inflammation will also cause systemic clotting in the capillaries of the body. Clotting can reduce the blood flow to the body organs, and cause the organs to fail. Examples or organ failure include: low blood pressure, lung failure, kidney failure, metabolic acidosis (build up of acids in the body) or coagulopathy (clotting disorder).

If a patient develops organ failure as a result of infection, they are described as having "Severe Sepsis", provided that we can correct the organ failure by giving the patient a lot of fluid. If the patient continues to have low blood pressure after receiving lots of fluid, the patient will need drugs to raise the blood pressure and correct the shock. The patient now has the most severe form of sepsis, called Septic Shock. Septic Shock is a very serious complication of infection.